This invention relates to a knife cylinder for cross-cutting or cross-perforating a continuous web such as paper, plastic, metal, foil, fabric or the like. The knife cylinder is formed with at least one open slot for receiving a knife substantially parallel to the axis of rotation of the cylinder and includes pressure points distributed over the length of the knife for attaching the knife within the cylinder.
U.S. Pat. No. 2,341,503 discloses a sheet cutting mechanism in which a web of material travels through a gap formed between a pressure cylinder and a knife cylinder rotatable in a machine frame for cutting the web. The web loops at least in part around one of the two cylinders. Cutting knives are mounted on the knife cylinder, each knife being mounted for adjustably pre-loading the knife in a radial direction at least by relatively small amounts with respect to the knife cylinder. An adjustable wedge is utilized for this purpose together with resilient means such as a block of rubber. The use of rubber as the elastic medium and a wedge mounted on the cylinder has, however, the drawback that rubber can become hard during the service life thus altering its elasticity. And, the wedge can be only crudely adjusted so that the elasticity of the rubber is not totally utilized and the rubber block which presses the knife against the web or the backup cylinder is significantly higher than necessary so that the cutting edge of the knife is unnecessarily strained and quickly wears out. In addition, the wedge can be adjusted only when the cylinder is not rotating, a feature that renders accurate and fine adjustment of the knife more difficult.
In the knife cylinder disclosed in British Patent No. 878556, the knife blade is radially adjustable with the use of a wedge shifted with the aid of a screw. However, the shifting of the wedge to thus adjust the knife blade is possible only if the knife cylinder is idle and not rotating.
Similarly, radial adjustment of the knife blade of a knife cylinder in German Patent No. 1,264,237 is effected with the use of a turnscrew. However, such adjustment is only possible when the knife cylinder is not rotating.
U.S. Pat. No. 4,594,928, commonly owned herewith, discloses a knife cylinder which includes radially disposed pressure medium cylinders which transmit a force for bracing the knives securely within the knife cylinder.